Teach me about RC fuel?

JRaut

JRaut

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I'm currently working on building a 5-cylinder radial glow-plug engine (which I'm documenting in another thread).

This is just about my first foray into the world of RC fuel; internet search results range from pre-bottled fuel to full chemistry setups.

The set of drawings I'm working from calls for "Methanol with 3 to 5% Nitromethane".

There's separate oil system, so no need to add any oil to the mix.


General advice is more than welcome and appreciated, but I'm especially looking to figure out the following:

1. Is it as simple as buying some methanol and nitromethane, then mixing them in the appropriate ratios?
2. Mix by weight or volume?
3. Where does a regular fella pick up methanol or nitromethane, local to Minneapolis would be preferred. Online prices seem to be insane.
4. Has "RC fuel technology" advanced to a point where there's a better suited fuel than the recommended Meth+Nitro combination?


Hey @Dhal22, don't think I forgot that you offered to buy the fuel for the first test run!!
Dhal22 said:
That is incredible, pull this project off and I'll buy the fuel for the test run.
Click to expand...

1647530643252.jpeg
 
For a local source your best bet will be a shop that deals with radio controlled planes. Stop in and ask what they carry for nitromethane with no oil.

Sent from my Pixel 5 using Tapatalk
 
I would think you could use standard model racing glow plug fuel which has castor oil but wouldn't hurt anything
I assume it's expensive now, but cheaper than trying to roll your own
 
That's a pretty engine you've got there!

Methanol is getting tough to source for consumers in pure form (wood alcohol). A petroleum supplier is your best bet. Iso-Heet is sometimes substituted for pure methanol, because you can buy it at the auto parts store. Denatured alcohol (ethyl, grain alcohol) is easy to buy and should work on a methanol-spec engine. If you can find nitromethane in concentrated form, let me know...

I'd just get model aviation fuel in the nitro concentration needed. Oil will be good for your valves and rings or pistons. It leaves residue, but you already have nitric acid residue to deal with from the nitromethane, so no loss.
 
These guys seem to be the winning ticket:

They've got a bunch of pre-mixed options, but are also willing to make custom blends. Prices definitely seem more reasonable too**.

So I suppose the new question that arises is:
Most of their pre-mixed options seem to have about 20% oil + rust inhibitors and other additives.​
​
If I get a custom blend, should I get it with 0% oil, or have them put in (say) 10% or so for good measure?​
​
I'd defer to them to pick which other additives/inhibitors.​


** EDIT: Price works out to be about $30/gal for 5% nitro.
 
Last edited:
JRaut said:
They also sell mix constituents, including slightly diluted nitromethane.

Their website says that they won't ship pure nitro because of hazmat regulations, but they will ship 80% Nitro / 20% Methanol.

Fuel Components – FHS OILS

fhsoils.com fhsoils.com
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$30/gallon for spec-made fuel is on the level with pre-mixed fuel prices. That sounds like a deal. The 80/20 would work just fine for your needs too! Also, don't discount the value of an additive blend. While not expensive, they can produce a much smoother run out of an engine.

Your particular motor will determine whether lubricant is needed. It does not look like your valve shafts are oiled. If you have cast iron sleeves and iron rings, you might not need any more than the crankcase oil provides. If you run a ringless piston (with a coated or uncoated piston) it might be a good idea to use oil in the fuel. High RPM calls for better oiling, too.
 
I'm definitely leaning toward having them mix me up a blend (with whatever additives they think are appropriate).

Perhaps with a little bit of oil mixed in too.


The drawings suggest that no lubrication is required, and the details of the construction suggest that's the case as well:
  • Stainless steel valves riding in phosphor bronze valve guides. I don't think oil should be required here, but I can add a few drops before I start it up each time.
  • Pistons are aluminum. Each has 3 cast iron rings (2 compression and 1 oil). They ride in cast iron sleeves.
  • RPMs will probably max out in the neighborhood of 6k.
  • It'll probably only be used as a bench-run motor. Unless someone wants to build a plane for it, I'd be happy to lend it out.

How does one deal with nitro / oil residue? Do I need to disassemble and clean after each use, or can I just squirt some WD40 into the cylinders?


Thanks for the insight @pontiac428. Definitely helpful.
 
I would not mix my own.
Find a hobby shop, explain what you got.
my feeling is you are still going to want some oil in the mix. But less than normal.. The synthetics are generally low in oil..
Just for info, here in the USA we use nitro, and in europe they generally don't.
 
Just go to the hobby shop and they should have 5% Nitro glow fuel....It's a methanol/nitro blend with oil added, whether it be castor or synthetic based. Generally, RC model engines don't need a separate oil systems whether its 2-stroke or 4-stroke. No cleanup is necessary other that what gets on the outside surfaces, and whatever's behind the engine while running...leaves a mess of oily residue. Usually on the planes, you'd try to mount the exhaust pointed away from the plane as much as possible, but there's always some.

Beautiful work BTW!
 
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